relay contacts sticking

[readydave8]

2 3/way and 3 4/way switches to the coil on icecube relay, long runs of wire. Relay works a receptacle with lighting transformer plugged in. Often when switch is turned off transformer receptacle stays energized, they can tap relay to make contacts open.

Relay rated for 10 amps. Transformer is 2 circuit, 600 watt, reduces 120v to 12 v ( also has taps for 13, 14, and 15 volts). Loaded approx 135 watts on one circuit, somewhat less on the other (I can get more accurate figures if needed).

Tried changing the ice cube relay and the replacement did the same thing.

Any advice?

[nizak]

You mentioned long runs, what is your voltage at the coil?

[don_resqcapt19]

Try adding some load in parallel with the relay coil. Take a look at this document

[readydave8]

You mentioned long runs, what is your voltage at the coil?

Good question that I won't have an answer until the next time I or others are at jobsite.

I would have thought that voltage drop would have caused problem with coil making connection, not breaking, but see now that if its arcing when making connection could be "welding" contacts and they don't want to open?

[gar]

100928-2039 EST

Is your relay something like a P&B KUP-11? 10 A rating would imply silver-cadmium contacts. These are better than pure silver for high currents. Silver is better for low voltage.

You should not have a problem switching a 120 V AC circuit of 1200 W load. Three pole relays in this package are available and you should use this type model with all of the contacts in parallel.

If these are AC to DC to AC to DC voltage changing power supplies, in other words a switching power supply instead of just a plain transformer, then there would be large input capacitors and these could cause very high peak turn on currents. The contacts could weld on turn on.

If it is just a transformer, then the greatest arcing occurs on turn off. But in an AC circuit there is not a rapid build up of a mound on the contacts.

For roughly 40 years I have, on a number of machines, used a P&B KUP DPDT with 10 A contacts in parallel to switch a DC circuit of 1 A at 110 V with a very large inductive load. This is very severe service. The relay switches multiple times every 20 seconds. Typical life is 3 months to about a year. When switching a DC circuit there is a unidirectional transfer of metal from one contact to the other. This results in a conical mound on one contact and a corresponding conical cavity in the mating contact.

For your application I might suggest a GE RR type relay instead of the ice-cube, or a solid-state relay. The GE has an advantage that you can have as many control points as you want with simple wiring. I have upwards of maybe 50 of these relays in my house.

.

[hurk27]

Good question that I won't have an answer until the next time I or others are at jobsite.

I would have thought that voltage drop would have caused problem with coil making connection, not breaking, but see now that if its arcing when making connection could be "welding" contacts and they don't want to open?

Nope capacitive coupling from the long runs is holding in the coil, like was said, add a load to the coil such as a resistor, and it will go away, try touching a loaded meter such as a wiggy or volt-con to the coil terminals, and I'll bet it drops out. many ice cub relays have very high impedance coils, and can be held in by very little current.

[Jnas480]

I had same problem almost at a power plant.
The low-voltage wire that some one ran about 1,800 feet was in medium voltage and high voltage cable trays and tied in PLC .

Basically the long cable run is like a step-up transformer due to all the power cables around the low-voltage cable.


If the cable is shielded, ground it properly. There are other ways to reduce the stray voltage by resistors. (They must be sized properly)

Like Hurk27 said

Good Luck

[dicklaxt]

I'm confused again,what is a 2 circuit transformer?

dick

[dicklaxt]

Try adding some load in parallel with the relay coil. Take a look at this document

Nope capacitive coupling from the long runs is holding in the coil, like was said, add a load to the coil such as a resistor, and it will go away, try touching a loaded meter such as a wiggy or volt-con to the coil terminals, and I'll bet it drops out. many ice cub relays have very high impedance coils, and can be held in by very little current.

Agreed capacitive coupling between the long parallel control wires is the problem.A way to combat this is to have the circuit opening switch close to the voltage source and the coil,obviously with 2-3ways and 3-4ways you can't do this.If tapping on the relay works in this scenario then I believe the jarring of the relay is causing the contacts to momentarily open thus acting as a stop button located close to the source and dropping out the relay by breaking the control wire circuit continuity.If the system drops out and stays out then one of the switches is open, if it re energizes then the control circuit to the relay coil is intact(ie: all switches are in the closed state).

The interposing relay in Don's post would support this logic of breaking the circuit close to the source.

Thats my story and I'm sticking to it

[don_resqcapt19]

...If tapping on the relay works in this scenario then I believe the jarring of the relay is causing the contacts to momentarily open thus acting as a stop button located close to the source and dropping out the relay by breaking the control wire circuit continuity...

Dick,
I think the tapping of the relay causes it to open because the relay is operating at the very low end of the hold in current. The capacitive coupling is providing enough current to barely keep the relay closed. The physical force of tapping overcomes the magnetic force of the coil and it opens the circuit.